The present invention relates to a process for the repair of blast furnaces. More specifically, it relates to a method of repairing blast furnaces using a vertical remote controlled refractory gunning apparatus.
Blast furnaces are used to melt iron and cast the resulting product from the blast furnace in a molten form. While once a major source for the domestic production of steel, the number of blast furnaces operating in the U.S. has declined rapidly. In the late 1970's, approximately 120 furnaces operated in the U.S. Currently, there are 35 operating blast furnaces in the U.S. with the number expected to decline to between 20 and 30 by 1990.
While the number of blast furnaces has declined, the remaining furnaces are producing a steady amount of iron, which means that iron production per blast furnace per year is increasing. To maintain this continued increased production, the blast furnaces must be in operation for longer periods of time. Due to this increased working time, it is highly desirable to avoid a total shutdown of the blast furnace. Thus, there remains a need for an efficient process for maintaining a blast furnace which will allow the blast furnace to be repaired without an expensive, time-consuming, total shutdown.
A number of processes and devices for repairing various steel making vessels are known.
U.S. Pat. No. 4,577,385 discloses a method for repairing the wall of a combustion chamber, such as a coke oven. In the disclosed method, a lance containing a light generating optical system is introduced through a pre-existing opening into the inside of the combustion chamber.
U.S. Pat. No. 4,649,858 discloses a repairing apparatus for an industrial furnace which comprises a plasma spray gun capable of being moved in a three-dimensional direction relative to the area of the furnace wall to be repaired. By controlling the spray distance of the plasma flame, repairs can be made to uneven areas of damage.
In U.S. Pat. No. 4,150,176, the tubular refractory vessel is disposed so that the longitudinal axis running therethrough is horizontal and a moist refractory mass is slung onto the longitudinal or annular sections.
The vertical remote controlled refractory gunning apparatus disclosed in U.S. Pat. No. 3,799,445 is said to be useful for repairing stationary furnaces and is introduced through the top of the stationary furnace.
The refractory gunning device disclosed in U.S. Pat. No. 4,181,258 is also introduced through the top of a stationary furnace.
According to Col. 4, lines 12-22 of U.S. Pat. No. 4,272,018, the disclosed refractory spraying device is lowered into the vessel to be sprayed.
U.S. Pat. No. 4,211,367 discloses a refractory gunning device that may be used in a blast. furnace while the walls are still at elevated temperatures. The disclosed device is preferably lowered into the blast furnace. See Col. 10, lines 54-65 and see also U.S. Pat. No. 4,272,020.
Other methods of repairing blast furnaces are also used. For instance, long pipe gunning is a manual method wherein multiple openings are created in the blast furnace shell and refractory is gunned onto the stack wall at various angles, producing significant amounts of rebound (wasted refractory that does not adhere).
Manual gunning requires a complete shutdown of the furnace. After the furnace has cooled, men must enter the furnace on erected scaffolds and gun the stack at close range.
Grouting, or the use of injectable refractories, requires that a refractory mixture be pumped through nozzles that have been mounted on the outside stack wall. Refractory material then fills the void between the burden (stack of raw materials) and the shell. The effectiveness of this method is questionable.
Thus, there remains a need for effective, on-line repair and maintenance method for blast furnaces.